We have conducted pre-clinical and clinical experiments with improved recombinant immunotoxins molecules for adult patient with solid tumors. LMB-9: is a disulfide stabilized immunotoxin composed of the variable regions of the monoclonal antibody B3 (dsFv) linked to a mutant form of Pseudomonas exotoxin, termed PE38. The disulfide bond renders the molecule very stable at 37oC when incubated in human serum. A Phase I clinical trial using this agent in adult patients with epithelial carcinomas is presently being carried out. Sixteen patients have been treated at the doses ranging from 5 to 39Ag/kg every other day. The agent is thus far well tolerated, with grade I/II gastrointestinal side effects. Dose escalation is ongoing. Once the MTD is reached, a phase II tail study to treat patients with metastatic colo-rectal cancer will be amended to the protocol. LMB-1 and Rituximab: immunotoxins are highly immunogenic proteins. Our previous experience indicates that >90% of the patients develop antibodies against LMB-1 immunotoxin after only once cycle. These antibodies neutralize the activity of the immunotoxin, precluding a multiple course therapy. We are presently conducting a phase II clinical trial to study the ability of the chimeric anti-CD20 antibody Rituximab to suppress HAMA and HATA formation in cancer patients after treatment with immunotoxin LMB-1. Rituximab mediates complement and antibodyudependent cell-mediated cytotoxicity (ADCC) and has direct anti-proliferative effects against malignant B-cell lines. Prior experience with Rituximab indicates that after the first infusion, Rituximab rapidly and effectively depleted B cells from the peripheral blood circulation, with maximum effect within 3-4 days. B-cell levels remained nearly undetectable until approximately 6 months post-treatment, followed by slow gradual recovery. Accrual for this study is ongoing. Pre-clinical development of SSdsFvPE38, an anti-mesothelin immunotoxin to target carcinoma of the ovary and mesothelioma. SSdsFv(PE38) is a disulfide single chain immunotoxin that targets mesothelin, a differentiation antigen present on the surface of ovarian cancer and mesotheliomas. SSdsFv(PE38) is cytotoxic to cells expressing mesothelin (IC50 0.9ng/ml on A431K5 cells) and is capable of causing significant tumor regression in nude mice bearing a tumor xenograft. The expression of mesothelin on normal human tissue is restricted to mesothelial cells in the peritoneum, pleura and pericardium. Similar expression has been found in Cynomolgus monkeys, making this species ideal for pre-clinical toxicity studies. We conducted pilot studies to evaluate the toxicity of SSscFv(PE38) when administered to Cynomolgus monkeys. Doses up to 1.0 mg/kg x 3 of SSscFv(PE38) are well tolerated by Cynomolgus monkeys. Except for transient liver transaminase elevation, no specific organ toxicity was noted in this pilot study. A more extensive toxicology testing using rodents and larger number of Cynomolgus monkeys is presently being conducted in collaboration with NeoPharm. Phase I study using SSdsFv(PE38) for patients with advanced ovarian carcinoma and mesothelioma are planned for early 2000. Based on our previous clinical findings on the Imaging and Phase I study using mAb B3 radiolabeled with 111In and 90Y we have designed a follow up study of 90Y- B3 with autologous stem cell support for patients with metastatic breast carcinoma. The primary objectives of this study are to determine the dose-limiting toxicities and the maximum tolerated dose of 90Y-B3 when administered with stem cell support. 70 % of breast carcinomas express the B3 antigen. Secondary objectives are to evaluate the anti-tumor activity and the immunogenicity of this agent when given in marrow ablative doses. The study has been recently approved by the NCI Protocol Review and Monitoring Committee and will be open for accrual within 1-2 months.